Hydraulic machine with electronically controlled valves

ABSTRACT

A hydraulic machine includes a number of piston/cylinder units which are each controlled by valves positioned upstream and downstream. The valves are in turn activated by an electronic regulator to switch the hydraulic machine selectively into a pump operating mode and a motor operating mode. The regulator selectively switches the individual piston/cylinder units or unit groups separately from one another into individually selectable operating modes as a function of certain regulating variables.

The invention relates generally to a valve-controlled hydraulic machine as per the preamble of patent claim 1 and to a regulating method for a hydraulic machine of said type.

Such valve-controlled hydraulic machines are known for example from EP 1 537 333 B1. Said document presents a hydraulic machine of axial-piston or radial-piston type of construction, which hydraulic machine can be operated as a motor and as a pump, wherein the delivery or displacement volume can be adjusted in a virtually continuously variable manner by means of the valve control, with a stepped adjustment also being known in the prior art. In an exemplary embodiment according to said prior art, the hydraulic machine is designed as an axial piston machine, wherein a multiplicity of pistons arranged in a cylinder is supported on a rotatably mounted swashplate. Each of said pistons delimits, together with the associated cylinder chamber, a working chamber which can be connected by means of a low-pressure-side valve and a high-pressure-side valve to a pressure medium inlet or to a pressure medium outlet. In the known solution, the two valves are embodied in the form of electrically releasable or lockable check valves which can be actuated by means of the electric pump-motor controller and which can be operated in the respective working chamber in the so-called “full mode”, in the “partial mode” or in the “idle mode”. In this way, the delivery or displacement volume can in this particular case be adjusted from a maximum value to zero in a continuously variable manner.

By means of a control unit of the pump-motor controller, the hydraulic machine is operated in accordance with a regulating algorithm in order to obtain a total delivery volume flow (pump) or total displacement volume flow (motor) which is as pulsation-free as possible. Here, the volume flow adjustment often takes place by phase-gating control, though may also be performed by phase-chopping control.

Hydraulic machines with displacement/delivery volume that can be varied by means of the valve control are also referred to as digital displacement units (DDU). For such hydraulic machines, basically all positive displacement principles are conceivable. Piston machines, in particular of radial-piston type of construction, are however advantageous because these make it possible for the inlet and outlet for each positive displacement unit to be formed separately and to thus be actively controlled. Here, it may by all means be expedient to make a distinction between pump and motor operation, such that then the control element may differ in appearance for the low-pressure and high-pressure connections.

In order, for example, to increase the prevailing hydraulic pressure in a hydraulic system such as is illustrated inter alia in FIG. 2, the hydraulic machine of the type of construction described above is switched to the pump mode, whereby pressure medium is fed into the system. In said mode, however, excess amounts of pressure medium cannot be extracted from the system by the hydraulic machine which is operating as a pump. That is to say any excess pressure medium can then be removed from the system only through the consumers, through leakage, by means of additional pressure accumulators, etc.

If a very fast pressure build-up in the system is required, it is accordingly necessary for the maximum pressure medium flow rate that can be delivered by the hydraulic machine (in the “full mode”) to be delivered as quickly as possible. This however may lead to overshoots in the pressure profile owing to an excess of pressure medium which is dependent on the regulation inertia. The pressure medium, however, can be removed from the system only through the abovementioned leakage or through the different consumers, which ultimately leads to a slow decay of the system pressure to the setpoint value. In other words, if the regulator demands a set value below zero (which may be the case if the pressure in the system reaches a very high value), then the DDU unit shuts off the volume flow (all piston-cylinder units are switched to idle) because a negative delivery rate is not possible in pump operation. Therefore, if the positive pressure in the system is too high, pressure is dissipated only via the components in the system. The inherent dynamics of said pressure dissipation are however dependent on the system and the operating point thereof, and are therefore difficult to regulate.

In the light of this present situation, it is an object of the present invention to provide a hydraulic machine of the above-specified generic type and a regulating method for said hydraulic machine in order to enable a setpoint pressure to be set more accurately.

Said object is achieved by means of a hydraulic machine having the features of patent claim 1 and by means of a method having the method steps of patent claim 7. The subclaims relate to advantageous refinements of the invention.

The basic concept of the invention consists in the present operating mode in which a hydraulic machine (preferably DDU) is operating being switched not as a whole but rather partially, that is to say for at least one selected piston/cylinder unit, as a function of a deviation of a detected actual value from a setpoint value, and thus the hydraulic machine being operated simultaneously partially in a pump operating mode and partially in a motor operating mode. Within the operating modes, it is then also possible, if appropriate individually or in accordance with the operating mode, to regulate for full-load, part-load or idle operation.

Accordingly, according to the invention, a hydraulic machine has a number of piston/cylinder units which can be controlled in each case by means of valves positioned upstream and downstream, which valves in turn can be activated by means of an electronic regulator so as to switch the hydraulic machine selectively into a pump operating mode and/or a motor operating mode. It is provided here that the regulator selectively switches the individual piston/cylinder units or unit groups separately from one another into individually selectable or selected operating modes.

The switching of the working mode of targetedly selected piston/cylinder units (pump to motor or motor to pump) in order to be able to switch from positive pressure medium delivery (pump operation) to negative pressure medium delivery (motor operation) (depending on the demand/specification of a preferably digital pressure regulator) has the advantage of considerably improved controllability of the hydraulic machine. Since the actuator means (pump/motor) can operate in the positive and (simultaneously partially) in the negative range, it is possible for faster regulation operations to be realized, which deliver pressure medium as quickly as possible. If, as a result, an excessively high pressure is generated in the system (overshoots), this can be actively dissipated (fast dissipation) by the regulating actuator, without the need to wait until the system has consumed the excess amount of pressure medium.

According to one aspect of the invention, it is provided that, within the operating mode individually selected for selected piston/cylinder units or unit groups, the regulator selectively switches into full-load or part-load operation. In other words, an adjustment of the displacement and/or delivery volume of the piston/cylinder units is performed individually or in groups exclusively for the selected and/or the non-selected units. In this way, it is possible for a pressure dissipation in the event of an overshoot, or a pressure build-up in the event of an undershoot, to be realized in a finely regulated manner.

The regulation of the hydraulic machine may furthermore preferably be aligned with the regulation of the consumers of the system (delivery rate of the pump and displacement volume of the motor may be coordinated with one another), whereby the regulation as a whole is improved.

Furthermore, a hydraulic system is conceivable which has a plurality of volume flow sources (pumps) of in each case different size. A superordinate regulator/monitoring means could detect possible pressure overshoots in the system and decide which DDU should switch which piston-cylinder unit into motor operation—with the aim of keeping pulsations in the system as small as possible. It is pointed out here that, if piston-cylinder units of different rated size are provided, it is made possible to calculate which of said piston-cylinder units is/are used to remove a certain amount of pressure medium (for example hydraulic oil, coolant etc.) from the system.

The regulating method according to claim 7 sees the following basic

-   -   detection of an actual pressure value in a hydraulic system         connected to the hydraulic machine or of a torque value,     -   comparison of the actual pressure value or actual torque value         (at a drive shaft for the piston-cylinder units) with a setpoint         value, and determination of a deviation, and     -   switching of the present operating mode individually for         selected or selectable piston-cylinder units or unit groups of         the hydraulic machine as a function of the deviation.

Said method can be used in particular in a hydraulic machine (DDU) having the features of the preamble of patent claim 1.

The invention will be explained in more detail below on the basis of a preferred exemplary embodiment and with reference to the appended figure.

FIG. 1 shows a preferred exemplary embodiment of a pressure regulator with a DDU/DVR unit in which the individual cylinders can be freely switched between pump and/or motor operation,

FIG. 2 shows the exemplary construction of a hydraulic machine, in the present case of radial-piston type of construction, and

FIG. 3 shows a pressure regulator with a DDU/DVR unit according to the prior art for comparison.

FIG. 1 shows a pressure regulator according to the invention having a hydraulic machine, preferably a DDU/DVR unit 1, composed substantially of an electrical/electronic machine regulator 2 with an input interface 4 for the input of a setpoint pressure value for a hydraulic system 6 (for example a construction machine) and an output interface 8 to which the DDU-DVR unit 1 (hydraulic machine) is connected.

The hydraulic machine 1 may be for example a valve-controlled piston machine (axial-piston or radial-piston machine) which can be operated in the pump mode and/or motor mode with variable delivery and/or displacement volume. Such a piston machine as illustrated by way of example in FIG. 2 has, as per the description already given in the introduction with regard to the prior art, a multiplicity of pistons 10 which are guided slidingly in separate cylinder pressure chambers 12 and which are controlled by means of individually assigned low-pressure valves 14 and high-pressure valves 16. The low-pressure valves 14 connect the pressure chambers 12, which can in each case be varied in volume by the piston 10, to a pressure medium tank 18, whereas the high-pressure valves 16 connect the respective pressure chambers 12 for example to a consumer or consumers of the hydraulic system 6, wherein further hydraulic regulating elements (not shown) may be interposed between the consumers and the hydraulic machine 1.

DDU units basically permit a fast switch of the operating mode of the hydraulic machine from the pump mode to the motor mode and vice versa. Furthermore, as already stated above, it is possible for the hydraulic machine, within the selected operating mode, to be switched into a full-load operating mode, any desired part-load operating mode or an idle operating mode.

Provision is now made according to the invention for the operating mode of individual piston/cylinder units 10 within the hydraulic machine 1 to be switched from pump operation to motor operation or vice versa as a function of the detected pressure conditions in the hydraulic system 6. That is to say, if, in the case of pump operation for increasing the prevailing pressure in the system 6 to a setpoint pressure, an excessive amount of pressure medium is fed into the hydraulic system 6 (overshoot behaviour), it is possible according to the invention for one or even several (selected) cylinder/piston units 10 of the (same) hydraulic machine 1 to be switched into the motor operating mode, with full-load or part-load operation additionally correspondingly selected if appropriate. Said piston/cylinder unit(s) 10 of the hydraulic machine 1 can then remove the excess amount of pressure medium from the system 6 (preferably hydraulic system) in a fast and controlled manner.

Since it is accordingly the case that the actuator means of the system (of the hydraulic machine) can operate individually both in the positive range (delivering pressure medium) and also in the negative range (consuming/discharging pressure medium), it is possible for the regulator 2 to be designed for the individual control of the individual piston/cylinder units 10 or of selected unit pairs in order to attain the desired setpoint pressure value quickly.

It is pointed out at this juncture that the above regulator 2 for the targeted switch of individual cylinder/piston units 10 in the pump operating mode of the hydraulic machine 1 from pump operation to motor operation also functions, in principle, in the reverse direction in the motor operating mode of the hydraulic machine 1, specifically from motor operation to pump operation. That is to say, if it is sought to dissipate a system pressure to a certain pressure, the hydraulic machine 1 is switched into the motor operating mode. In the case of a regulation-induced undershooting of the setpoint pressure, according to the invention, the regulator 2 actuates individually selected piston/cylinder units 10 or unit pairs so as to switch said selected units 10 into the pump operating mode, with full-load operation or part-load operation also being selectable if appropriate, and thus increase the system pressure to the desired setpoint pressure (undershooting is prevented or quickly compensated). This regulating process, specifically the switching from motor operation to pump operation as per the above statements, applies in particular for torque regulation, whereby a hydraulic motor initially generates a torque on the shaft and then torque (components) are dissipated from the shaft by means of the switch to pump operation. This yields improved regulation characteristics.

There is consequently disclosed a hydraulic machine (DDU unit) 1 with a number of piston-cylinder units 10 which can be controlled in each case by means of valves 14, 16 positioned upstream and downstream, which valves in turn can be activated by means of an electronic regulator 2 so as to switch the hydraulic machine 1 selectively into a pump operating mode and/or a motor operating mode. According to the invention, the regulator selectively switches the individual piston/cylinder units 10 or unit groups separately from one another into individually selectable operating modes as a function of certain regulating variables. 

1. A hydraulic machine comprising: a number of valves; an electronic regulator configured to activate the number of valves so as to switch the hydraulic machine selectively into a pump operating mode and a motor operating mode; and a number of piston/cylinder units which are controlled by the number of valves positioned upstream and downstream, wherein the regulator is configured to selectively switch the piston/cylinder units as individual piston/cylinder units or unit groups separately from one another into individually selectable operating modes.
 2. The hydraulic machine as claimed in claim 1, further comprising: a setpoint pressure input device configured to predefine a setpoint pressure for the regulator, wherein the regulator is configured to switch the hydraulic machine as a whole into one of the pump operating mode and the motor operating mode in accordance with the setpoint pressure.
 3. The hydraulic machine as claimed in claim 2, further comprising: a pressure sensor configured to detect an actual pressure value; and a comparator configured to determine a deviation between the detected actual pressure value and the predefined setpoint pressure value, wherein the regulator is configured to select the piston/cylinder units of the hydraulic machine individually or in groups and to switch the selected piston/cylinder units into a different selected operating mode based on the deviation.
 4. The hydraulic machine as claimed in claim 3, wherein, within the operating mode individually selected for selected piston/cylinder units or unit groups, the regulator is configured to selectively switch into one of full-load operation and part-load operation.
 5. The hydraulic machine as claimed in claim 3, wherein, the regulator is configured to switch the selected piston-cylinder units or unit groups selectively into the motor operating mode and to leave unselected piston-cylinder units in the pump operating mode when the hydraulic machine is in the pump operating mode.
 6. The hydraulic machine as claimed in claim 3, wherein the regulator is configured to switch the selected piston-cylinder units or unit groups selectively into the pump operating mode and to leave unselected piston-cylinder units in the motor operating mode when the hydraulic machine is in the motor operating mode.
 7. The hydraulic machine as claimed in claim 1, wherein the regulator is configured to adjust one of a pressure, a torque and a volume flow rate.
 8. A regulating method for the selective operation of a hydraulic machine, which has a multiplicity of piston/cylinder units, in a pump or motor operating mode, comprising: detecting one of an actual pressure value and an actual torque value in a hydraulic system connected to the hydraulic machine; comparing the one of the actual pressure value and the actual torque value with a setpoint value and determining a deviation; and switching a present operating mode individually for selected piston-cylinder units or unit groups as a function of the deviation.
 9. The regulating method as claimed in claim 8, further comprising: adjusting at least one of a displacement and a delivery volume of the piston/cylinder units individually or in groups exclusively for at least one of the selected piston/cylinder units and the non-selected units. 